Accuracy for key parameters in modelling study
Authors: Bingyi Yang, Yun Lin, Benjamin J Cowling
Journal: The Lancet Public Health (2022)

Billy Quilty and colleagues1Quilty BJ Clifford S Hellewell J et al.Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study.Lancet Public Health. 2021; 6: e175-e183Summary Full Text Full Text PDF PubMed Scopus (63) Google Scholar did a modelling study of quarantine and testing effectiveness, which was informed by key epidemiological parameters. Although we believe their overall implications could still hold true, some key measurements and results might be subject to underestimation due to parameterisation of the duration of viral shedding. Quilty and colleagues1Quilty BJ Clifford S Hellewell J et al.Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study.Lancet Public Health. 2021; 6: e175-e183Summary Full Text Full Text PDF PubMed Scopus (63) Google Scholar defined the duration of viral shedding as the time from infection until viral shedding stops, which, by definition, also includes the incubation period—the time between infection and the onset of symptoms (figure). In the model by Quilty and colleagues,1Quilty BJ Clifford S Hellewell J et al.Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study.Lancet Public Health. 2021; 6: e175-e183Summary Full Text Full Text PDF PubMed Scopus (63) Google Scholar a mean of 17 days (SD 0·94) was assumed for the duration of viral shedding for symptomatic individuals, with reference to a systematic review.2Cevik M Tate M Lloyd O Maraolo AE Schafers J Ho A SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.Lancet Microbe. 2021; 2: e13-e22Summary Full Text Full Text PDF PubMed Scopus (510) Google Scholar However, the study by Cevik and colleagues2Cevik M Tate M Lloyd O Maraolo AE Schafers J Ho A SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.Lancet Microbe. 2021; 2: e13-e22Summary Full Text Full Text PDF PubMed Scopus (510) Google Scholar mostly reviewed the duration between symptom onset and viral shedding cessation, which excluded the incubation period; therefore, it could underestimate the duration of viral shedding in Quilty's model. We simulated the models that parameterised viral shedding duration since infection (proposed by Quilty and colleagues1Quilty BJ Clifford S Hellewell J et al.Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study.Lancet Public Health. 2021; 6: e175-e183Summary Full Text Full Text PDF PubMed Scopus (63) Google Scholar) and symptom onset (reviewed by Cevik and colleagues2Cevik M Tate M Lloyd O Maraolo AE Schafers J Ho A SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.Lancet Microbe. 2021; 2: e13-e22Summary Full Text Full Text PDF PubMed Scopus (510) Google Scholar), using values reported by previous studies (figure).2Cevik M Tate M Lloyd O Maraolo AE Schafers J Ho A SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis.Lancet Microbe. 2021; 2: e13-e22Summary Full Text Full Text PDF PubMed Scopus (510) Google Scholar, 3McAloon C Collins Á Hunt K et al.Incubation period of COVID-19: a rapid systematic review and meta-analysis of observational research.BMJ Open. 2020; 10e039652Crossref Scopus (191) Google Scholar We modelled a faster clearance of viral shedding when parameterising shedding duration since infection (median 11 days, IQR 10–12) compared with since symptom onset (median 13 days, IQR 11–15). This led to underestimation of the infectiousness period (defined by Quilty and colleagues as periods with cycle threshold lower than 30; mean 7·6 days [SD 1·5]1Quilty BJ Clifford S Hellewell J et al.Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study.Lancet Public Health. 2021; 6: e175-e183Summary Full Text Full Text PDF PubMed Scopus (63) Google Scholar vs mean 10·1 days [SD 2·5] from our simulation, for symptomatic individuals) and therefore the transmission potential averted (figure). Key epidemiological parameters (eg, incubation period and duration of viral shedding) vary depending on the SARS-CoV-2 variants and vaccination history,4Kissler SM Fauver JR Mack C et al.Viral dynamics of SARS-CoV-2 variants in vaccinated and unvaccinated persons.N Eng J Med. 2021; 385: 2489-2491Crossref PubMed Scopus (51) Google Scholar, 5Hay JA Kissler SM Fauver JR et al.Viral dynamics and duration of PCR positivity of the SARS-CoV-2 Omicron variant.medRxiv. 2022; (published online Jan 14.) (preprint).https://doi.org/10.1101/2022.01.13.22269257Google Scholar calling for regular assessment and fine-tuning of various public health measures, such as quarantine periods. BJC reports honoraria from AstraZeneca, Fosun Pharma, GlaxoSmithKline, Moderna, Pfizer, Roche, and Sanofia Pasteur, and receives support from the [email protected] programme of the Innovation and Technology Commission of the Hong Kong SAR Government. All other authors declare no competing interests. Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling studyTesting might allow for a substantial reduction in the length of, or replacement of, quarantine in the control of onwards transmission from contacts of SARS-CoV-2-infected individuals. Decreasing test and trace delays and increasing adherence will further increase the effectiveness of these strategies. Further research is required to empirically evaluate the potential costs (increased transmission risk, false reassurance) and benefits (reduction in the burden of quarantine, increased adherence) of such strategies before adoption as policy. Full-Text PDF Open Access